This invention relates to miscible blends of amide-and/or imide-containing polymers and polyarylates or arylate-carbonate copolymers and to a method for improving the miscibility of such blends. The blends are useful in the manufacture of extruded sheet, high temperature connectors, aircraft and mass transportation vehicle interiors, injection molded articles, and extruded profiles and thermoformable articles.
Aromatic polycarbonmides, by which is meant polyamides, polyimides and poly(amide-imides), may be viewed as a single class of polymers. Typically, these well-known aromatic polymers are high melting, high glass-transition temperature resins which exhibit excellent mechanical properties and heat resistance and very good chemical resistance. The main drawback of these materials is the fact that they are often extremely difficult to process. For example, the polyamide which may be described as the product of the self-condensation of p-aminobenzoic acid is always spun from solution, using powerful solvents such as sulfuric acid (nearly anhydrous or oleum), chlorosulfonic acid, fluorosulfonic acid, or combinations of lithium chloride with phosphorus compounds such as N,N-dimethyldimethyl phosphinamide and the like. Spinning may also be accomplished using nitrogen-containing solvents, such as, for example, N,N,N.sup.1 N.sup.1 -tetramethylurea, optionally in combination with an inorganic salt.
Better solubility characteristics are encountered with aromatic polyamides that are not wholly para-linked. The high molecular weight polyamide prepared via the reaction of isophthaloyl chloride with m-phenylene diamine is soluble in chloroform. However, these polyamides are also very difficult to melt-process.
Polyamides possessing a flexibilizing oxygen bridge within their molecules, such as the polyamides based on 2,2-bis(4-(4-aminophenoxy)phenyl propane and iso-and/or terephthaloyl chlorides are said to have improved melt-fabricability characteristics. These resins exhibit good thermal stability, good electrical and mechanical properties, and can be molded into useful shapes, even though the moldability is still poor. The ease of fabrication may be improved by plasticizing these polyamides using, for example, various bisphthalimides, siloxanes and the like. Processibility may also be improved by blending with poly(aryl ether sulfones) or with polyarylates, as described in Japanese Patent Applications 58/52,348 and 58/52,347.
Aromatic polyimides are also a well known, and are described for example by Cassidy in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 18, pp. 704-719. In general, polyimides, and especially aromatic polyimides, have excellent heat resistance but are difficult to process. The same is generally true of aromatic poly(amide-imides). Thus, according to P. E. Cassidy et al. (cited above), "wholly aromatic polyimide molding powders must be fabricated by sintering at high temperature and pressure". Injection molding and extrusion are ordinarily not possible. J. M. Aducci in Polyimides, K. L. Mittal, Editor, 1984, published by Plenum Press, New York, states on page 1024:
"Polyimides, produced by the chemical reaction of an aromatic dianhydride and an aromatic diamine, were the first of the aromatic thermally stable polymers introduced in the mid-1950's. Polyimides did not behave as thermoplastics even though they had linear structures. Polymer backbones comprised of rigid, inherently stable, aromatic phenylene and imide rings imparted polyimides with excellent thermal oxidative properties and at the same time made them exceedingly difficult to process because of their high and sometimes indeterminate melting points." PA1 "The most commonly used method for establishing miscibility in polymer-polymer blends or partial phase mixing in such blends is through determination of the glass transition (or transitions) in the blend versus those of the unblended constituents. A miscible polymer blend will exhibit a single glass transition between the Tg's of the components with a sharpness of the transition similar to that of the components. In cases of borderline miscibility, broadening of the transition will occur. With cases of limited miscibility, two separate transitions between those of the constituents may result, depicting a component 1-rich phase and a component 2-rich phase. In cases where strong specific interactions occur, the Tg may go through a maximum as a function of concentration. The basic limitation of the utility of glass transition determinations in ascertaining polymer-polymer miscibility exists with blends composed of components which have equal or similar (20.degree. C. difference) Tg's whereby resolution by the techniques to be discussed of two Tg's is not possible." PA1 "Perhaps the most unambiguous criterion of polymer compatibility is the detection of a single glass transition whose temperature is intermediate between those corresponding to the two component polymers."
According to T. P. Gannett et al., in U.S. Pat. No. 4,485,140, the polyimide of the structural formula: ##STR1## where R.sub.5 and R.sub.6 are --CH.sub.3 or --CF.sub.3, is typical of aromatic polyimides which are generally infusible. According to Alberino et al., U.S. Pat. No. 3,708,458, a polyimide having recurring units of the formula: ##STR2## "possesses highly useful structural strength properties but . . . is difficult to mold, by compression at elevated temperatures, because of its relatively poor flow properties in the mold". These patentees also disclose polyimides having included in the polymer backbone a certain proportion of the reaction product of 3,3',4,4'-benzophenone tetracarboxylic dianhydride with 2,4- or 2,6-toluene diamine (or the corresponding diisocyanates). The copolymers are described as having better flow properties in the mold even though such difficult molding procedures "as sintering or hot processing" were the criteria used.
Thus, it can be said that aromatic imide-based polymers in general do not lend themselves easily to melt fabrication except perhaps by compression molding.
The processability of some of these imide-based materials may be improved by blending or alloying them with other resins which are themselves more readily melt processable and thereby more easily thermoformed and injection molded. For example, U.S. Pat. No. 4,293,670 to Robeson et al., discloses blends of polyarylether resins and polyetherimide resins having excellent mechanical compatibility and good impact strength and environmental stress crack resistance. U.S. patent application Ser. No. 537,042 filed on Sept. 29, 1983 in the name of J. E. Harris et al., assigned to the present assignee, describes blends of a selected polyaryl-ketone and a polyetherimide. U.S. patent application Ser. No. 626,105 filed on June 29, 1984 in the name of J. E. Harris et al., assigned to the present assignee, describes blends of a poly(amide-imide) and of a poly(aryl ether ketone). In addition, U.S. Pat. No. 4,258,155 describes blends of poly(amide-imides) with polyetherimides.
Although polyarylates have been known in the technical literature since 1957, they have only recently become widely available from commercial sources. Polyarylates are polyesters derived from a dihydric phenol and at least one aromatic dicarboxylic acid, such as, for example, the polyarylate based on bisphenol A and a mixture of terephthalic and isophthalic acid. The processing and properties of polyarylates is described by L. M. Maresca and L. M. Robeson in "Engineering Thermoplastics: Properties and Applications", ed. by J. M. Margolis, p. 255, Marcel Dekker, Inc., New York, 1985. Arylate copolymers containing carbonate linkages in addition to the aromatic ester groups are also known. Phosgene or other carbonate-generating species are used along with the diacids and bisphenols for their preparation.
Blends of polyarylates with other polymers are the subject of several patents, including U.S. Pat. Nos. 4,231,922; 4,246,381; 4,259,458; and 3,946,091. U.S. Pat. No. 4,250,279 discloses blends of polyarylates with poly(etherimides), including blends of a particular polyarylate and a particular poly(etherimide) that are said to be miscible over a narrow range.
Miscibility in polymer blends may confer certain advantages. For example, such blends tend to be transparent, possess a single glass transition temperature and exhibit other characteristics of a single material. By varying the relative proportions of the blend components mechanical properties can be tailored to meet the requirements of a particular application without losing transparency and other desirable characteristics generally typical of single phase materials.
In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. According to authorities:
(A) "It is well known that compatible polymer blends are rare". Wang and Cooper, Journal of Polymer Science, Polymer Plastics Edition, Vol. 21, p. 11 (1983).
(B) "Miscibility in polymer-polymer blends is a subject of widespread theoretical as well as practical interest currently. In the past decade or so, the number of blend systems that are known to be miscible has increased considerably. Moreover, a number of systems have been found that exhibit upper and lower critical solution temperatures, i.e., complete miscibility only in limited temperature ranges. Modern thermodynamic theories have had limited success to date in predicting miscibility behavior in detail. These limitations have spawned a degree of pessimism regarding the likelihood that any practical theory can be developed that can accommodate the real complexities that nature has bestowed on polymer-polymer interactions". Kambour, Bendler and Bopp, Macromolecules, 1983, Vol. 16, p. 753.
(C) "The vast majority of polymer pairs form two-phase blends after mixing can be surmised from the small entropy of mixing for very large molecules. These blends are generally characterized by opacity, distinct thermal, transitions, and poor mechanical properties. However, special precautions in the preparation of two-phase blends can yield composites with superior mechanical properties. These materials pay a major role in the polymer industry, in several instances commanding a larger market than either of the pure components. Olabisi, Robeson, and Shaw, Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 7.
(D) "It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible with other thermoplastic polymers, the discovery of a homogeneous mixture of partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently, unpredictable with any degree of certain; P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, p. 555." Younes, U.S. Pat. No. 4,371,672.
(E) "The study of polymer blends has assumed an ever increasing importance in recent years and the resulting research effort has led to the discovery of a number of miscible polymer combinations. Complete miscibility is an unusual property in binary polymer mixtures which normally tend to form phase-separated systems. Much of the work has been of qualitative nature, however, and variables such as molecular weight and conditions of blend preparation have often been overlooked. The criteria for establishing miscibility are also varied and may not always all be applicable to particular systems." Saeki, Cowie and McEwen, Polymer, 1983, Vol. 25, January, p. 60.
Thus miscible blends are not common. The criteria for determining whether or not two polymers are miscible are now well established. According to Olabisi et al., Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 120:
W. J. MacKnight, et al., in Polymer Blends, D. R. Paul and S. Newman, eds., 1978, published by Academic Press, New York, N.Y., state on page 188:
In this passage, it is clear from the omitted text that by compatibility the authors means miscibility, i.e., single phase behavior. See, for example, the discussion in Chapter 1 by D. R. Paul in the same work.
As a specific example of how difficult it is to predict a priori the miscibility of polymers, let us take an example from U.S. Pat. No. 4,258,155. Example 8 shows that the poly(amide-imides) ##STR3## and the polyetherimide ##STR4## are miscible as evidenced by the single Tg of the blends. However, as described in European Patent Application 016,354, the closely related poly(amide-imide) copolymer ##STR5## is not miscible with the polyetherimide above even though it contains 50 mole percent of the identical amide-imide repeat units.
Along related lines, U.S. Pat. No. 4,340,697 describes blends of aromatic poly(amide-imides) and thermoplastic resins selected from the group consisting of a polyphenylene sulfide resin, a polysulfone resin, a polyamide resin, an aromatic polyester resin, a polyphenylene ether resin, and a phenoxy resin. Compositions with improved moldability characteristics are obtained; yet, in spite of a rather large number of systems examined, the patent does not mention that truly miscible alloys were uncovered.
Miscible blend compositions comprising polyarylates and amide and/or imide containing polymers would be a useful advance in the resin art.